1. Field of the Invention
The present invention relates generally to fluid-filled vibration-damping devices capable of exhibiting damping effect on the basis of flows of fluid sealed therein. More specifically, the present invention is concerned with a fluid-filled vibration-damping device of novel structure, which is suitably applicable to an engine mount, a body mount, a suspension bushing and other equipments for use in automotive vehicles, for example. The present invention is also concerned with a novel manufacturing method of the fluid-filled vibration-damping device.
2. Description of the Related Art
A fluid-filled vibration-damping device is known as one type of a vibration-damping device, which is interposed between two members of a vibration system so as to flexibly connect these two members or mount one of these members on the other member in a vibration-damping fashion. The fluid-filled vibration-damping device includes a fluid-sealing area filled with a non-compressible fluid and subjected to a vibrational load applied thereto, and exhibits damping effect on the basis of flows of the non-compressible fluid within the fluid-sealing area, in the event of application of a vibrational load to the fluid-sealing area. Attempts have been made for applying the fluid-filled vibration-damping device to an engine mount, a body mount, a suspension bushing, and other equipments for use in automotive vehicles. As one measure of further improvement of damping characteristics of the fluid-filled vibration-damping device, it has been proposed to put a predetermined volume of gas into the fluid-sealing area. An example of such a fluid-filled vibration-damping device is disclosed in the following patent publications 1 and 2, and other publications, for example.
[Patent Publication 1]
JP-A-8-54038
[Patent Publication 2]
JP-A-60-139507
In the fluid-filled vibration-damping device as disclosed in the above-listed publications, damping characteristics vary depending on a volume of gas put into the fluid-sealing area. For this reason, important is a precise control of the volume of gas injected into the fluid-sealing area. For mass production, important are of course to facilitate a manufacturing method of the vibration-damping device, as well as to simplify manufacturing facilities.
However, the above-mentioned importance have not been taken into account enough, upon designing the known fluid-filled vibration-damping device of conventional structure.
More specifically, the fluid-filled vibration-damping device disclosed in patent publication 1, has a structure in which a plurality of members are mutually assembled within a mass of a non-compressible fluid to provide the fluid-sealing area, and one of the members is formed with a large recess open to the fluid-sealing area with its opening facing vertically downwardly so that a volume of gas is retained in the large recess. However, the fluid-filled vibration-damping device disclosed in patent publication 1 is not provided with a special structure to make a volume of gas retained in the large recess constant. This makes it extremely difficult to control the volume of gas put into the fluid-sealing area. As one means of control of the volume of gas contained in the fluid-sealing area, it would be conceivable to inject a given volume of gas from an external area into the fluid-sealing area filled with the non-compressible fluid. This means, however, additionally needs a special equipment for measuring and injecting a given volume of gas, resulting in complicated manufacturing facilities, and making it difficult to manufacture the fluid-filled vibration-damping device due to increased number of steps of manufacture.
The above-listed patent publications 1 and 2 disclose another means to hold the volume of gas contained in the fluid-sealing area in constant. According to this means, a ball-shaped member of hollow structure made of an elastic layer is filled with a given volume of gas, and then is housed within the fluid-sealing area filled with the non-compressible fluid. This means, however, additionally needs special apparatus and methods of manufacturing the ball-shaped structure, making it difficult to actually practice this means. Additionally, the presence of the elastic layer of the ball-shaped structure separates the given volume of gas contained in the ball-shaped structure from the non-compressible fluid, possibly deteriorating intended damping effect expected by putting the gas into the non-compressible fluid.